This invention relates to dispensing devices for multi-component liquid mixtures. More specifically, this invention relates to guns for mixing reactive foam components or like fluid products in a controlled stoichiometric ratio and dispensing the resultant mixture at a controlled constant or variable flow rate.
Urethane foams are widely used in the construction and building trades. They are used, for example, as insulation materials, as support materials in walls, partitions, and the like, as underlayment supports for pipelines, and as waterproof insulating sealants for cracks and fissures.
In a common practice, the urethane foam is formed at the job site by mixing reactive liquid foam components and immediately thereafter applying the resultant reactive mixture to the intended substrate. As and after they are applied, the components of the mixture undergo reaction to produce the desired foam. The foaming which occurs upon reaction expands the applied reactive mixture so as to facilitate complete coverage of the substrate or complete filling of an open area which is to be filled or sealed. In general, the use of urethane foams provides a relatively convenient, effective, and inexpensive method of insulating, sealing, or filling a variety of substrate materials and structures.
Various devices have been proposed for mixing and dispensing the reactive foam components. These devices generally are in the form of "guns" which include manually activated valves which are intended to control the flow of the reactive components into a mixing chamber in the gun from which the resultant mixture is discharged. The respective components are initially retained under pressure in separate vessels which are connected by flexible tubing to inlet ports on the gun which, in turn, lead to the valve assembly. The mixing chamber is preferably detachable and disposable, inasmuch as residual material in the chamber can solidify and clog the chamber and its entry and exit ports.
Among features and functions which are desirable in such dispensing guns are (a) the ability to control the flow rate of the respective liquid components and, concomitantly, the rate at which the reactive mixture is dispensed, thereby permitting application of optimal amounts of the mixture and compensation for any decreasing head pressure as the components are dispensed from their respective pressurized vessels; (b) a capability in the gun for consistently and uniformly mixing the respective component streams at a desired volume ratio, thereby facilitating reaction of the components in a desired stoichiometric ratio; (c) light weight and favorable handling and operating characteristics, particularly in a manual operation of trigger assemblies for actuating the valves; and (d) ease and economy of manufacture. In general, the dispensing guns heretofore provided have proven to be unsatisfactory in one or more of the above respects.